Magnetic Field-Induced Lattice Effects in a Quasi-2D Organic Conductor Close to the Mott Metal-Insulator Transition

TL;DR

This study investigates how magnetic fields influence lattice properties in a quasi-2D organic conductor near the Mott transition, revealing a field-insensitive Mott transition and a field-induced magnetic phase transition with strong magneto-elastic coupling.

Contribution

The paper reports the first high-resolution dilatometric measurements showing magnetic-field-induced phase transition and magneto-elastic effects in a quasi-2D organic Mott insulator.

Findings

Mott transition temperature is unaffected by magnetic fields up to 10 T.

A magnetic-field-induced phase transition occurs above 1 T along the interlayer axis.

Strong magneto-elastic coupling is evidenced by the phase transition.

Abstract

We present ultra-high-resolution dilatometric studies in magnetic fields on a quasi-two-dimensional organic conductor $\kappa$-(D8-BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br, which is located close to the Mott metal-insulator (MI) transition. The obtained thermal expansion coefficient, $\alpha(T)$, reveals two remarkable features: (i) the Mott MI transition temperature $T_{MI}$ = (13.6 $\pm$ 0.6)\,K is insensitive to fields up to 10\,T, the highest applied field; (ii) for fields along the interlayer \emph{b}-axis, a magnetic-field-induced (FI) phase transition at $T_{FI}$ = (9.5 $\pm$ 0.5)\,K is observed above a threshold field $H_c \sim$ 1 T, indicative of a spin reorientation with strong magneto-elastic coupling.